Itinerant to localized transition of electrons in the antiferromagnetic superconductor UPdAl

Fujimori, Shinichi   ; Saito, Yuji  ; Okane, Tetsuo  ; Fujimori, Atsushi*; Yamagami, Hiroshi*; Haga, Yoshinori   ; Yamamoto, Etsuji  ; Onuki, Yoshichika*

In heavy Fermion (HF) compounds, electrons show both itinerant and localized behaviour depending on temperature. Above the characteristic temperature , their magnetic properties are well described by the completely "localized" -electron models. On the other hand, well below , their Fermi surfaces (FS's) have been explained well by the "itinerant" -electron model. These two models assume totally different natures of -electrons, and how they transform between these states as a function of temperatures has never been understood on the level of their electronic structures. Here we have studied the band structure of the HF antiferromagnetic superconductor UPdAl well below and above by angle-resolved photoelectron spectroscopy (ARPES), and have found that the -bands, which form the FS's at low temperatures, are excluded from FS's at high temperatures.